This invention relates to a large image display apparatus in which such images as television video signals or image signals are displayed on a display board including a large number of display elements.
In a conventional display apparatus of this type, a large number of incandescent lamps, cathode ray tubes or discharge lamps are used as the display elements. However, such prior art display apparatus using the incandescent lamps is not satisfactory in that the operating life of the incandescent lamps is relatively short, the lamps consume a large amount of power and generate a large quantity of heat, thus requiring a large and expensive cooling means. Furthermore, a cathode ray tube is not only expensive, but also produces an insufficient quantity of light. Another prior art apparatus using discharge lamps is relatively inexpensive and provides sufficient luminance, thus achieving high luminous efficacy. However, a current limiting element is required to turn on the discharge lamp, and the following problem thus occurs. When the discharge lamp is turned on with a DC voltage, a resistor must be used as the current limiting element and power consumption is increased due to the use of the resistor. When the discharge lamp is turned on with a commercial AC voltage, an inductor or capacitor can be used as the current limiting element. However, prior art apparatus of this type have poor response characteristics for video signals.
Engineers, including the present inventors, disclosed a large image display apparatus in Japanese Patent Disclosure No. 59-19995 (corresponding to U.S. Pat. No. 4,635,052). According to this apparatus, discharge lamps are used as display elements which are turned on with a high frequency voltage. The apparatus has low power consumption and high response to video signals, and at the same time, is compact and light. However, since the discharge lamps are turned on with an AC voltage, preheating filaments are required for both electrodes so as to instantaneously turn on the discharge lamps. For this reason, power consumption cannot be sufficiently decreased.